Psoriasis is a chronic, immune-mediated disease affecting 1-3% of the population worldwide (Jacobson and Kimball, Epidemiology: Psoriasis In: Psoriasis and Psoriatic Arthritis (Eds: Gordon K B, Ruderman E M). Springer-Verlag Berlin Heidelberg, Germany; 2005:47-56), with the greatest disease prevalence occurring in North America and Europe (Krueger and Duvic, J. Invest. Dermatol, 102:145-185, 1994). The most common form of psoriasis is plaque-type psoriasis, present in 65-86% of patients and characterized by the presence of thick, scaly plaques. Based on the National Psoriasis Foundation's definitions of moderate to severe psoriasis, the prevalence of moderate to severe psoriasis in the United States is estimated at 0.31% of persons age 18 or older (Stem et al., J. Investig. Dermatol. Symp. Proc. 9:136-139, 2004). Patients with psoriasis report reduction in physical functioning and mental functioning comparable to that observed in patients with cancer, arthritis, hypertension, heart disease, diabetes, and depression (Rapp et al., J. Am. Acad. Dermatol. 41(3Pt1):401-407, 1999). In a US survey of the impact of psoriasis on quality of life, respondents reported difficulties in the workplace, difficulties socializing with family members and friends, exclusion from public facilities, difficulties in getting a job, and contemplation of suicide (Krueger et al., Arch. Dermatol., 137:280-284, 2001).
Traditionally, treatment for psoriasis has included medications that suppress the growth of skin cells. Treatment approaches for psoriasis often include creams and ointments, oral medications, and phototherapy.
In recent years, biologic response modifiers that inhibit certain cytokines have become a potential new avenue of treatment for psoriasis patients. For example, tumor necrosis factor (TNF) is a cytokine involved in inflammatory response and scientific evidence suggests it plays a fundamental role in the pathogenesis of psoriasis (Kreuger et al. (2004) Arch Dermatol 140:218; Kupper (2003) N Engl J Med 349:1987). The advent of targeted biologic therapies has made a significant impact on the treatment options for psoriasis, including moderate to severe psoriasis. In the United Kingdom, for example, the National Institute for Health and Clinical Excellence (NICE) recommends etanercept, a human recombinant TNF receptor fusion protein, for patients with moderate to severe psoriasis who have failed conventional therapies. Etanercept is not, however, effective in every patient. Thus, there remains a need for more effective treatment options in patients suffering from psoriasis.